1. Field of the Invention
The present invention relates generally to elevator systems, and more particularly to an elevator safety rescue system permitting the elevator car of a rack and pinion elevator system to be lowered slowly in the event of malfunction.
2. Description of the Related Art
Rack and pinion drive elevator systems are often used to power elevators installed in industrial applications, including relatively high structures, e.g., industrial elevators installed in tall towers used for broadcast communications towers, smoke stacks, bridge towers, etc., or in relatively deep excavations such as mines. Rack and pinion elevator systems are free of the height limitations particularly affecting hydraulic elevators and also affecting cable elevator systems to a lesser degree.
These rack and pinion drive elevators are of course required to have safety features analogous or equivalent to elevators using other lift and propulsion principles, i.e., cable and hydraulically powered elevators. It is of course absolutely essential that any elevator include a system that prevents the elevator from falling in the event of power failure or lift malfunction. In the cases of hydraulic and particularly cable type elevators, where loss of hydraulic pressure or cable breakage could allow an essentially free fall of the elevator cab, various braking systems have been developed and are required to be included in such installations. Rack and pinion drive elevators are also required to have an overspeed elevator safety device, but the principles are somewhat different, in that the drive system pinion gear is positively engaged with the gear rack at all times such that slowing or stopping rotation of the pinion drive motor(s) by means of a motor braking system also slows or stops movement of the elevator; such systems are inherently free of any danger of slippage. Additionally, the rack and pinion drive configuration can allow for an additional safety rescue lowering device that can allow for the safe self rescue of a stranded car.
Any time the emergency system stops the elevator due to some malfunction in the system, there exists the issue of safe rescue for the elevator and its passengers and freight to a safe landing or location. Historically, this is accomplished by actuation of a mechanism causing the electric drive motor brakes to slip, thus allowing the elevator to descend gradually. However, the heat generated from slipping brakes can be considerable, particularly in the case of relatively tall elevators. Moreover, the heating of the brakes reduces their capacity, causing a restriction of operational use to a few minutes or approximately thirty feet before overheating occurs. This may be acceptable for a short height installation. However, elevators installed in tall industrial locations or mines may have landing levels with distances between landings of many times those between landing levels on short height installations, thus preventing a safe and effective rescue using a slip brake system due to the heat buildup and resulting reduction in braking capacity in such a system.
Thus, an elevator safety rescue system solving the aforementioned problems is desired.